1. Field of the Invention
The present invention relates to an image pick-up device or video camera for use in a television camera, and more particularly to a diaphragm control optimizing the light amount for a subject.
2. Description of the Related Art
A previously known video camera for the television camera serves to set a photometric or light lo measuring area at the center of the field of image to be picked up, and has a function of controlling the diaphragm of the lens in accordance with only the light amount within the photometric area so as to control the light amount automatically (this function is generally called ALC (Auto Lens Control)).
In such a video camera, the lens diaphragm is not closed even if light is incident on the outside of the light measuring area. Under the condition of backlight, therefore, this camera can pick up the image of a subject against an optimum amount of light as long as the subject is located within the photometric area, as disclosed by Sudoh et al. in JP-A-62-281683.
However, in the conventional video camera, the photometric area is fixed only at the center area. Thus, if the television camera is set so that the subject is located outside the photometric area, an ALC circuit does not operate properly. As a result, the subject cannot be picked up clearly. Namely, under the condition of backlight, the subject will darken.
An improved video camera is disclosed by Nita at al. in JP-A-2-25178 in which the photometric area in the image field can be moved both in the vertical and horizontal directions and the iris is controlled based on the luminance of the subject irrespective of the light source in the field. But the disclosed video camera is not operated in easy way and it cannot obtain a good picture with a natural tone considering background lights.